Role of renalase in the regulation of blood pressure and the renal dopamine system. Curr Opin Nephrol Hypertens. 2011;20:31-36. [PMID: 21099685 DOI: 10.1097/mnh.0b013e3283412721]

Relation Between Exposure to Tobacco Smoke Assessed by Serum Cotinine Concentration and Questionnaire Method, and Serum Renalase Concentration-the Importance of the Coexistence of Arterial Hypertension and Other Cardiovascular Diseases

Exposure to tobacco smoke (ETS) is one of the main risk factors for cardiovascular disease (CVD). Renalase is a protein that may play a role in the pathogenesis of CVD. The aim of the study was to assess the relationship between ETS and serum renalase concentration. A group of 109 patients was recruited for this study (49.7 ± 14.7 years). In accordance with the questionnaire, patients were divided into the following subgroups: subgroup A- declaring themselves active smokers (n = 36), subgroup B- declaring themselves non-smokers and exposed to environmental tobacco smoke (n = 35), subgroup C- declaring themselves non-smokers and not exposed to environmental tobacco smoke (n = 38). The same patients were divided based on cotinine concentration into the following subgroups: subgroup D- active smokers (n = 42), subgroup E- non-smokers exposed to environmental tobacco smoke (n = 66), and subgroup F- non-smokers not exposed to environmental tobacco smoke (n = 1). Serum cotinine concentration and serum renalase concentration were measured using ELISA tests. Serum renalase concentration was statistically significantly higher in subgroup C than in subgroups A and B and in subgroup E and F than in D. There was a negative correlation between serum cotinine concentration and serum renalase concentration (r = -0.41, p < 0.05). Regression analysis showed that higher BMI, higher diastolic blood pressure, coronary artery disease and higher serum cotinine concentration are independent risk factors of lower serum renalase concentration. The questionnaire method of assessing exposure to tobacco smoke was characterized by high sensitivity, but only moderate specificity, especially in terms of assessing environmental exposure to tobacco smoke. In summary, the study showed an independent relationship between exposure to tobacco smoke and lower serum renalase concentration.

Renalase Potential as a Marker and Therapeutic Target in Chronic Kidney Disease

Hypertension and cardiovascular disease are prominent features of chronic kidney disease, and they are associated with premature mortality and progression toward end-stage kidney disease. Renalase, an enzyme secreted predominantly by the kidney and identified in 2005, seems to be one of the missing pieces in the puzzle of heart and kidney interaction in chronic kidney disease by lowering blood pressure and reducing the overactivity of sympathetic tone. This review aims to summarize evidence from clinical studies performed on subjects with CKD in order to explore the value of renalase as a marker and/or a therapeutic target in this disease.

Coexistence of Cardiovascular Risk Factors and Blood Renalase Concentration

Cardiovascular diseases (CVDs) are one of the biggest health challenges facing health systems around the world. There are certain risk factors (CVRFs) that contribute to CVD. Risk factors associated with lifestyle such as tobacco consumption are particularly essential. Renalase is a recently discovered flavoprotein that may be involved in the progression of cardiometabolic diseases. The aim of the study was to investigate the relation between CVRFs and blood renalase concentration (BRC). The study group consisted of 96 people (51% women) who were hospitalized in the internal medicine department. CVRFs were measured using the AHA Life 7 scale. The E3109Hu ELISA kit was used to assess BRC. We found higher BRC in groups with a lower number of CVRFs (p < 0.05). We found a negative correlation between BRC and the number of CVRFs (r = -0.41). With the regression analysis, obesity, smoking, and a lack of physical activity (LoPE) were independently associated with lower blood renalase concentration. ROC analysis indicated the highest accuracy of BRC < 38.98 ng/mL in patients with ≥5 CVRFs. In conclusion, patients with a higher number of CVRFs had lower BRCs. The CVRFs particularly associated with a lower BRC were obesity, smoking, and LoPE.

Korean fermented soybean paste (Doenjang) has anti-obesity and anti-hypertensive effects via the renin-angiotensin system (RAS) in high-fat diet-induced obese rats

The health-beneficial outcomes of doenjang, a Korean fermented food have been questioned due to its high salt content; moreover, the detailed underlying mechanisms of its health beneficial effects are not fully investigated. Thus, this study aimed to investigate doenjang's anti-obesity effects, anti-hypertensive effects, and its underlying mechanisms in high-fat diet -induced obesity. Sprague-Dawley rats fed with normal diet (ND), high-fat diet (HD), HD with 8% additive salt (HDS), or HD with doenjang containing 8% salt (HDJ) for 13 weeks. Compared to HD and HDS groups, the HDJ group had lower body and epididymal fat tissue weight gain and showed hypotrophy and hypoplasia. The RAS-related mRNA levels in the adipose tissue, including Renin and Ace were downregulated in the HDJ group compared to HD and HDS groups. Additionally, HDJ groups had significant improvements in systolic blood pressure, serum RAS-associated parameters (e.g., angiotensin II and aldosterone), renal mRNA levels related to RAS (e.g., angiotensin II receptor type 1 and 2), and aldosterone-associated mRNA expressions (e.g., mineralocorticoid receptor) in the kidney of HD-induced obese rats. Most importantly, HDS and HDJ groups showed distinct outcomes regarding adipogenesis and electrolytes metabolism, even though both diets contain a high level of salt. HDS group showed a higher epididymal fat tissue weight, mass, and adipocyte size than HDJ group. In addition, compared with HDJ group, HDS group significantly decreased the release of Na+ and K+ throughout the urine and feces. The present study addresses that doenjang has anti-obesity effects and anti-hypertensive effects by activating RAS in the adipose tissue and kidney, respectively. Additionally, this study also demonstrates that salt in doenjang and the additive salt differently influences adipogenesis and electrolytes metabolism, supporting doenjang has health advantageous effects regardless of its high salt contents.

Renalase: a novel regulator of cardiometabolic and renal diseases

Renalase is a ~38 kDa flavin-adenine dinucleotide (FAD) domain-containing protein that can function as a cytokine and an anomerase. It is emerging as a novel regulator of cardiometabolic diseases. Expressed mainly in the kidneys, renalase has been reported to have a hypotensive effect and may control blood pressure through regulation of sympathetic tone. Furthermore, genetic variations in the renalase gene, such as a functional missense polymorphism (Glu37Asp), have implications in the cardiovascular and renal systems and can potentially increase the risk of cardiometabolic disorders. Research on the physiological functions and biochemical actions of renalase over the years has indicated a role for renalase as one of the key proteins involved in various disease states, such as diabetes, impaired lipid metabolism, and cancer. Recent studies have identified three transcription factors (viz., Sp1, STAT3, and ZBP89) as key positive regulators in modulating the expression of the human renalase gene. Moreover, renalase is under the post-transcriptional regulation of two microRNAs (viz., miR-29b, and miR-146a), which downregulate renalase expression. While renalase supplementation may be useful for treating hypertension, inhibition of renalase signaling may be beneficial to patients with cancerous tumors. However, more incisive investigations are required to unravel the potential therapeutic applications of renalase. Based on the literature pertaining to the function and physiology of renalase, this review attempts to consolidate and comprehend the role of renalase in regulating cardiometabolic and renal disorders.

A case report of renal calyceal diverticulum with hypertension in children and review of literature

Background

Renal calyx diverticulum refers to a cystic lesion covered with the transitional epithelium in the renal parenchyma. Although there is no clear evidence that calyx diverticulum can cause hypertension, there exists a close association between the two, and there are few related reports. Herein, we reported the case of a child with renal calyx diverticulum complicated with hypertension and summarized the diagnosis and treatment.

Case presentation

Physical examination of the patient, an 11-year-old child, revealed a left renal cyst with hypertension (155/116 mmHg). There were no related symptoms. Routine urine and blood biochemical examinations showed no abnormalities. Imaging revealed left renal cyst compression causing the hypertension. She underwent renal cyst fluid aspiration and injection of a sclerosing agent into the capsule, but her blood pressure increased again 3 days postoperatively. Color Doppler ultrasonography showed that the size of the left renal cyst was the same as that preoperatively. To further confirm the diagnosis, cystoscopic retrograde ureteropyelography was performed to confirm the diagnosis of renal calyx diverticulum. Subsequently, renal calyceal diverticulum resection and calyx neck enlargement were performed. The operation went smoothly and the blood pressure returned to normal postoperatively. No abnormalities were noted at the 7-month postoperative follow-up.

Conclusion

There exists an association between renal calyx diverticulum and hypertension. Therefore, hypertension can be considered a surgical indication for renal calyx diverticulum. Moreover, renal calyceal diverticulum in children can be easily misdiagnosed as a renal cyst. Therefore, it is important to be vigilant to prevent a series of complications, such as postoperative urine leakage, in such cases.

A new biomarker (RENALASE) for the diagnosis of blunt renal trauma in an experimental study

INTRODUCTION

Kidneys are the most frequently injured organ in the genitourinary system, but there is no specific biological marker for this trauma. Renalase may be a descriptive biomarker of the pathology that causes renal ischemia, nephrotoxicity, and acute renal failure.

OBJECTIVE

This study investigated the role of serum and urine levels of renalase for the diagnosis of renal injury in rats with experimentally induced blunt renal trauma.

STUDY DESIGN

Thirty 3-month-old Sprague-Dawley adult male rats were divided into five groups (n = 6) as follows: control (Group 1), sham (Group 2), right nephrectomy (Group 3), left renal trauma (Group 4), and right nephrectomy plus left renal trauma (Group 5). Serum samples were acquired 3, 24 and 48 h post-trauma, and urine samples were acquired between 0-24 and 24-48 h post-trauma. Changes in serum and urine levels of renalase, dopamine, epinephrine, metanephrine, normetanephrine, urea, and creatinine were assessed after blunt renal trauma.

RESULTS

No significant changes in serum levels of these compounds were observed at 3 h post-trauma in Groups 1 and 2 or in urine collected sequentially at 0-24 and 24-48 h. By contrast, levels of renalase, dopamine, metanephrine, and normetanephrine in serum increased during hour 3 in Groups 4 and 5. Moreover, increases in urine levels of renalase, dopamine, epinephrine, metanephrine, and normetanephrine were observed at hours 0-24 in Groups 4 and 5.

DISCUSSION

A definitive diagnosis of traumatic renal injury in children is made with contrast-enhanced computed tomography. However, the scan results in high doses of radiation exposure to children. Here, we report for the first time that renalase levels may be useful as a biomarker for the diagnosis of renal injury due to blunt renal trauma.

CONCLUSION

Renalase may be a simple, effective, and noninvasive biomarker that indicates traumatic renal injury. It could be used as an adjunct for evaluation, particularly for isolated traumatic renal injury in cases where access to computed tomography is not straightforward.

Reinvestigation of the tonic natriuretic action of intrarenal dopamine: comparison of two variants of salt-dependent hypertension and spontaneously hypertensive rats

The intrarenal dopamine system has been thoroughly investigated at all levels, especially its role in salt-dependent and other forms of hypertension. However, the evidence regarding dopamine's tonic influence on renal tubular transport of sodium remains equivocal. We reinvestigated its tonic influence on sodium excretion and systemic and renal haemodynamics. Early effects of dopamine D1 receptor blockade using 90-min Schering 23390 (SCH) infusion were examined in anaesthetized rats on 7 days' high salt diet (HS), early uninephrectomized rats on 14 days' HS diet, drinking 1% saline (HS/UNX), and in spontaneously hypertensive rats (SHR). In the HS group (baseline BP ~133 mm Hg) renal intracortical SCH promptly decreased sodium, water and total solute excretion (UNa V, V, Uosm V), with significant difference from the solvent-infused group. BP and renal artery blood flow (RBF, Transonic probe) did not change. In HS/UNX model (baseline BP ~150 mm Hg), characterized by hypertrophy of the remaining kidney, the excretion parameters only tended to decrease whereas SCH induced an ~20% fall in RBF. In SHR (BP ~180 mm Hg), UNa V and V tended to increase in solvent-infused rats; this increasing tendency was abolished by SCH infusion. During experiments the renal vascular resistance increased significantly in SCH- and solvent-infused SHR. Despite some contradictory findings regarding the genuine tonic control of renal excretion by intrarenal dopamine, our results clearly support such role in rats on HS diet and in SHR, the model resembling human essential hypertension. The observations strengthen the experimental basis and the rationale for targeting the intrarenal dopamine system in attempts to combat arterial hypertension.

High Salt Diet Impacts the Risk of Sarcopenia Associated with Reduction of Skeletal Muscle Performance in the Japanese Population

The World Health Organization has recommended 5 g/day as dietary reference intakes for salt. In Japan, the averages for men and women were 11.0 g/day and 9.3 g/day, respectively. Recently, it was reported that amounts of sodium accumulation in skeletal muscles of older people were significantly higher than those in younger people. The purpose of this study was to investigate whether the risk of sarcopenia with decreased muscle mass and strength was related to the amount of salt intake. In addition, we investigated its involvement with renalase. Four groups based on age and salt intake ("younger low-salt," "younger high-salt," "older low-salt," and "older high-salt") were compared. Stratifying by age category, body fat percentage significantly increased in high-salt groups in both younger and older people. Handgrip strength/body weight and chair rise tests of the older high-salt group showed significant reduction compared to the older low-salt group. However, there was no significant difference in renalase concentrations in plasma. The results suggest that high-salt intake may lead to fat accumulation and muscle weakness associated with sarcopenia. Therefore, efforts to reduce salt intake may prevent sarcopenia.

Roles and mechanisms of renalase in cardiovascular disease: A promising therapeutic target

Cardiovascular disease (CVD) is prevalent worldwide and remains a leading cause of death. Although substantial progress has been made in the diagnosis and treatment of CVD, the prognosis remains unsatisfactory. Renalase is a newly discovered cytokine that is synthesized by the kidney and then secreted into blood. Numerous studies have suggested the efficacy of renalase in treating CVD by metabolizing catecholamines in the circulatory system. As a new biomarker of heart disease, renalase is normally recognized as a signalling molecule that activates cytoprotective intracellular signals to lower blood pressure, protect ischaemic heart muscle and promote atherosclerotic plaque stability in CVD, which subsequently improves cardiac function. Due to its important regulatory role in the circulatory system, renalase has gradually become a potential target in the treatment of CVD. This review summarizes the structure, mechanism and function of renalase in CVD, thereby providing preclinical evidence for alternative approaches and new prospects in the development of renalase-related drugs against CVD.

Potential Impact of MicroRNA Gene Polymorphisms in the Pathogenesis of Diabetes and Atherosclerotic Cardiovascular Disease

MicroRNAs (miRNAs) are endogenous, small (18–23 nucleotides), non-coding RNA molecules. They regulate the posttranscriptional expression of their target genes. MiRNAs control vital physiological processes such as metabolism, development, differentiation, cell cycle and apoptosis. The control of the gene expression by miRNAs requires efficient binding between the miRNA and their target mRNAs. Genome-wide association studies (GWASs) have suggested the association of single-nucleotide polymorphisms (SNPs) with certain diseases in various populations. Gene polymorphisms of miRNA target sites have been implicated in diseases such as cancers, diabetes, cardiovascular and Parkinson’s disease. Likewise, gene polymorphisms of miRNAs have been reported to be associated with diseases. In this review, we discuss the SNPs in miRNA genes that have been associated with diabetes and atherosclerotic cardiovascular disease in different populations. We also discuss briefly the potential underlining mechanisms through which these SNPs increase the risk of developing these diseases.

Circulating renalase predicts all-cause mortality and renal outcomes in patients with advanced chronic kidney disease

BACKGROUND/AIMS

Patients with chronic kidney disease (CKD) have been found to show markedly increased rates of end-stage renal disease, major adverse cardiovascular and cerebrovascular events (MACCEs), and mortality. Therefore, new biomarkers are required for the early detection of such clinical outcomes in patients with CKD. We aimed to determine whether the level of circulating renalase was associated with CKD progression, MACCEs, and all-cause mortality, using data from a prospective randomized controlled study, Kremezin STudy Against Renal disease progression in Korea (K-STAR; NCT00860431).

METHODS

A retrospective analysis of the K-STAR data was performed including 383 patients with CKD (mean age, 56.4 years; male/female, 252/131). We measured circulating renalase levels and examined the effects of these levels on clinical outcomes.

RESULTS

The mean level of serum renalase was 75.8 ± 34.8 μg/mL. In the multivariable analysis, lower hemoglobin levels, higher serum creatinine levels, and diabetes mellitus were significantly associated with a higher renalase levels. Over the course of a mean follow-up period of 56 months, 25 deaths and 61 MACCEs occurred. Among 322 patients in whom these outcomes were assessed, 137 adverse renal outcomes occurred after a mean follow-up period of 27.8 months. Each 10- μg/mL increase in serum renalase was associated with significantly greater hazards of all-cause mortality and adverse renal outcomes (hazard ratio [HR] = 1.112, p = 0.049; HR = 1.052, p = 0.045). However, serum renalase level was not associated with the rate of MACCEs in patients with CKD.

CONCLUSION

Our results indicated that circulating renalase might be a predictor of mortality and adverse renal outcomes in patients with CKD.

Direct laboratory evidence that pregnancy-induced hypertension might be associated with increased catecholamines and decreased renalase concentrations in the umbilical cord and mother’s blood

Background

Renalase (RNL) is a controversial enzyme as to whether it oxidizes catecholamines (CAs) (as is generally accepted) in the blood or not. CAs (dopamine [DPMN], epinephrine [EPI] and norepinephrine [NEPI]) are associated with hypertension, including pregnancy-induced hypertension, which occurs in 8–10% of all pregnancies. Therefore, the aim of the study was to compare CAs and renalase concentration in (i) normotensive controls (C), (ii) patients with preeclampsia (PE) and (iii) patients with severe preeclampsia (SPE), which is one of the well-known symptoms of hypertension.

Methods

This case-control study involved 90 women divided into three groups – 30 C, 30 PE and 30 SPE – whose age and body mass indexes (BMIs) were similar. A total of 270 blood samples (90 maternal samples, 90 umbilical cord artery samples and 90 umbilical cord vein samples) were obtained. CAs and RNL concentrations of the biological samples were measured by enzyme-linked immunosorbent assay (ELISA).

Results

Comparing the amounts of CAs, RNL and systolic blood pressure (SBP)/diastolic blood pressure (DBP) between healthy control pregnant women and pregnant women with PE and SPE (SBP/DBP was 120/80 mm Hg for C, above 140/90 mm Hg for PE and above 160/110 mm Hg for SPE), the levels of CAs were significantly increased whereas RNL was reduced. The correlation between SBP/DBP and the amount of RNL in pregnant women with PE and SPE was negative.

Conclusions

These novel results are evidence that hypertension seen in PE and SPE is directly related to increased levels of CAs and reduced RNL concentrations. The use of RNL preparations may be preferred in future to prevent maternal and perinatal morbidity and mortality due to pregnancy-induced hypertension.

Investigation of Renalase gene rs2576178 polymorphism in patients with coronary artery disease

Renalase gene rs2576178 polymorphism has been demonstrated to be a risk factor of ischemic stroke, essential hypertension, and end-stage renal disease, but the association Renalase with risk of coronary artery disease (CAD) has been less reported. Therefore, we detected Renalase rs2576178 polymorphism in 449 CAD patients and 507 healthy controls using matrix-assisted laser-desorption ionization (MALDI)/time of flight (TOF)-mass spectrometry (MS). It was found that GG genotype or G allele of rs2576178 polymorphism was associated with the risk of CAD. Stratified analysis indicated that Renalase polymorphism significantly increased the risk of CAD in females, smokers, and alcoholics. However, there was no significant association between different genotypes of rs2576178 polymorphism and clinical parameters. In summary, Renalase rs2576178 polymorphism is associated with increased risk of CAD, but this finding should be confirmed by larger studies with more diverse ethnic populations.

MIR146A rs2910164 (G/C) Polymorphism is Associated with Incidence of Preeclampsia in Gestational Diabetes Patients

Preeclampsia and gestational diabetes are common pregnancy disorders that may be interrelated. MIR146A rs2910164 (G/C) is a functional polymorphism that was associated with several diseases. This study aimed to investigate the frequency of rs2910164 polymorphism and its possible correlation with the incidence of preeclampsia in gestational diabetes patients. The study involved 250 pregnant women divided into 80 healthy control subjects, 85 gestational diabetes patients only, and 85 patients of gestational diabetes combined with preeclampsia. Systolic and diastolic blood pressures, urinary proteins, kidney and liver functions, glucose homeostasis parameters, and lipid profile were determined. Genotyping of the polymorphism was conducted by PCR-RFLP. The frequency of the minor C allele of rs2910164 polymorphism was significantly higher among patients of gestational diabetes combined with preeclampsia compared to the control group (p = 0.012) and the gestational diabetes group (p = 0.014). Patients of gestational diabetes and preeclampsia carrying CC genotype showed higher systolic and diastolic blood pressure, and increased urea, creatinine, urine protein, and dyslipidemia compared to the carriers of GG and GC genotypes. In conclusion, the results of the current study suggest that the rare CC genotype of MIR146A rs2910164 (G/C) polymorphism may be related to increased incidence of preeclampsia in gestational diabetes patients.

Serum Renalase Levels in Adolescents with Primary Hypertension

The prevalence of hypertension in pediatric populations continues to rise. Recent studies suggest that renalase plays an important role in blood pressure regulation. The aim of this study was to evaluate serum renalase concentrations in hypertensive children. This study was a prospective cohort analysis of 88 adolescents (40 girls; 48 boys) aged 11-18 years, divided into two groups: HT-38 subjects with primary hypertension; and R (reference group)-50 subjects with normal blood pressure. Serum renalase concentration was measured using a commercial enzyme-linked immunosorbent assay kit. Hypertensive patients had higher serum renalase levels (median 29.8 µg/mL; Q1-Q3: 26.1-35.8) than the reference group (median 26.8; Q1-Q3: 22.96-29.4, p < 0.01). Serum renalase was strongly related to serum uric acid levels. In hypertensive patients, serum renalase was positively correlated with 24-h systolic blood pressure (SBP) and 24-h diastolic blood pressure (DBP) and with 24-h SBP and 24-h DBP Z-score (LMS). Our results allow us to conclude that serum renalase correlates with blood pressure elevation. Special attention should be drawn to the correlation between renalase and serum uric acid levels not only in hypertensive, but also in normotensive teenagers. Further studies are needed to answer the question of whether increased serum renalase may be a predisposing factor to hypertension in normotensive patients with hyperuricemia.

The enzyme: Renalase

Within the last two years catalytic substrates for renalase have been identified, some 10 years after its initial discovery. 2- and 6-dihydronicotinamide (2- and 6-DHNAD) isomers of β-NAD(P)H (4-dihydroNAD(P)) are rapidly oxidized by renalase to form β-NAD(P)⁺. The two electrons liberated are then passed to molecular oxygen by the renalase FAD cofactor forming hydrogen peroxide. This activity would appear to serve an intracellular detoxification/metabolite repair function that alleviates inhibition of primary metabolism dehydrogenases by 2- and 6-DHNAD molecules. This activity is supported by the complete structural assignment of the substrates, comprehensive kinetic analyses, defined species specific substrate specificity profiles and X-ray crystal structures that reveal ligand complexation consistent with this activity. This apparently intracellular function for the renalase enzyme is not allied with the majority of the renalase research that holds renalase to be a secreted mammalian protein that functions in blood to elicit a broad array of profound physiological changes. In this review a description of renalase as an enzyme is presented and an argument is offered that its enzymatic function can now reasonably be assumed to be uncoupled from whole organism physiological influences.

Increased serum renalase in hemodialysis patients: is it related to left ventricular hypertrophy?

INTRODUCTION

Left ventricular hypertrophy (LVH) is one of the most common cardiac abnormalities in patients with end stage renal disease (ESRD). Hypertension, diabetes, increased body mass index, gender, age, anemia, and hyperparathyroidism have been described as risk factors for LVH in patients on dialysis. However, there may be other risk factors which have not been described yet. Recent studies show that renalase is associated with cardiovascular events. The aim of this study was to reveal the relation between renalase, LVH in patients under hemodialysis (HD) treatment.

METHODS

The study included 50 HD patients and 35 healthy controls. Serum renalase levels and left ventricle mass index (LVMI) were measured in all participants and the relation between these variables was examined.

FINDINGS

LVMI was positively correlated with dialysis vintage and C-reactive protein (CRP) (r = 0.387, p = 0.005 and r = 0.597, p < 0.001, respectively) and was negatively correlated with residual diuresis and hemoglobin levels (r = -0.324, p = 0.022 and r = -0.499, p < 0.001, respectively). There was no significant association of renalase with LVMI in the HD patients (r = 0.263, p = 0.065). Serum renalase levels were significantly higher in HD patients (212 ± 127 ng/mL) compared to controls (116 ± 67 ng/mL) (p < 0.001). Renalase was positively correlated with serum creatinine and dialysis vintage (r = 0.677, p < 0.001 and r = 0.625, p < 0.001, respectively).

DISCUSSION

In our study, LVMI was correlated with dialysis vintage, residual diuresis, CRP, and hemoglobin. LVMI tends to correlate with renalase and this correlation may be significant in studies with more patient numbers. The main parameters affecting renalase levels are dialysis vintage and serum creatinine.

A novel marker in pregnant with preeclampsia: renalase

BACKGROUND

Preeclampsia is characterized by an increase in high blood pressure and decrease in GFR and proteinuria, however, the underlying mechanisms are still unclear. Renalase is a recently discovered protein implicated in regulation of blood pressure in humans.

MATERIALS AND METHODS

Plasma concentrations of serum renalase were measured in healthy controls, healthy pregnant and pregnant with preeclampsia matched for age, gestational age, in the third trimester of pregnancy. Serum renalase levels were compared in pregnant with and without preeclampsia and non-pregnant controls. Factors associated with serum renalase levels in pregnancies were also evaluated.

RESULTS

In healthy pregnant serum renalase levels were significantly higher than in controls. However, pregnant with preeclampsia had lower renalase levels than healthy controls. Serum renalase levels were inversely associated with blood pressure levels and positively correlated with glomerular filtration rate.

CONCLUSION

The results indicated that the development of preeclampsia in pregnant is accompanied by altered serum renalase levels. High blood pressure and kidney damage that characterize this disorder are mediated at least in part by low renalase levels.

The efficacy of hemodialysis in interventional therapy in coronary artery disease patients with chronic renal insufficiency

The aim of this study was to explore the efficacy and safety of hemodialysis in interventional therapy for patients with coronary artery disease combined with chronic renal insufficiency. With the aging and social development, the number of coronary artery disease patients with chronic renal insufficiency gradually increased. Total 58 coronary heart disease patients with chronic renal dysfunction were selected. These patients were characterized with typical angina symptoms and typical electrocardiogram (ECG) changes of onset angina. Continuous oral administration of sodium bicarbonate tablets 1 g 3/day × 3 days and slow intravenous input sodium chloride 1000 ∼1500 mL 3-12 h before operation were given. By this way, all patients were treated by hydration and alkalization. After percutaneous coronary intervention (PCI) treatment, patients were immediately transferred to undergo 4 h of dialysis treatment without removing indwelling of femoral artery puncture sheath tube to protect renal function. Changes in renal function including serum creatinine, glomerular filtration rate, and urine were observed and recorded. All patients were successfully underwent PCI treatment. Within one month after PCI, there were no obvious complication and no stent thrombosis occurred. Among of 58 patients, 56 cases showed no significant increase in serum creatinine levels compared with those before operation. However, serum creatinine level of one patient increased to 251 umol/L and one patient still required permanent dialysis. Using hemodialysis in interventional therapy in coronary artery disease patients with chronic renal insufficiency could significantly improve the prognosis of the patients.

Ambulatory blood pressure and tubulointerstitial injury in patients with IgA nephropathy

Background

Few studies have been conducted to assess the ambulatory blood pressure (ABP) in IgA nephropathy (IgAN) patients. This study aimed to determine the relationships between ABP and renal histopathological findings assessed using the Oxford classification (OC) and the Japanese classification (JC), which have recently established histopathological criteria for IgAN.

Methods

This cross-sectional study included biopsy-diagnosed IgAN patients, in whom both a renal biopsy and ABP measurement were performed. The histopathological findings were assessed using the OC and the JC and were analyzed in relation to the ABP.

Results

A total of 111 IgAN patients were included. The score of interstitial fibrosis and tubular atrophy (T score) using the OC was a significantly associated factor with both the daytime and nighttime ABP values. In contrast, the other histopathological scores, including mesangial hypercellularity, endocapillary hypercellularity and segmental glomerulosclerosis, did not show significant associations with the ABP. The histological grade (H-grade) using the JC, which was based on the sum of injured glomeruli, was associated with the daytime ABP, but not with the nighttime ABP. The associations between the T score using the OC (%) and the daytime and nighttime ABP values were independent of age, gender, renal function, proteinuria and the use of antihypertensive medications, whereas the H-grade using the JC (%) did not show significant associations after adjusting for these clinical parameters.

Conclusions

These results suggest that the T score using the OC is the most relevant renal histopathological parameter associated with abnormalities of circadian blood pressure in IgAN patients.

Bacterial Renalase: Structure and Kinetics of an Enzyme with 2- and 6-Dihydro-β-NAD(P) Oxidase Activity from Pseudomonas phaseolicola

Despite a lack of convincing in vitro evidence and a number of sound refutations, it is widely accepted that renalase is an enzyme unique to animals that catalyzes the oxidative degradation of catecholamines in blood in order to lower vascular tone. Very recently, we identified isomers of β-NAD(P)H as substrates for renalase (Beaupre, B. A. et al. (2015) Biochemistry, 54, 795-806). These molecules carry the hydride equivalent on the 2 or 6 position of the nicotinamide base and presumably arise in nonspecific redox reactions of nicotinamide dinucleotides. Renalase serves to rapidly oxidize these isomers to form β-NAD(P)⁺ and then pass the electrons to dioxygen, forming H₂O₂. We have also shown that these substrate molecules are highly inhibitory to dehydrogenase enzymes and thus have proposed an intracellular metabolic role for this enzyme. Here, we identify a renalase from an organism without a circulatory system. This bacterial form of renalase has the same substrate specificity profile as that of human renalase but, in terms of binding constant (K(d)), shows a marked preference for substrates derived from β-NAD⁺. 2-dihydroNAD(P) substrates reduce the enzyme with rate constants (k(red)) that greatly exceed those for 6-dihydroNAD(P) substrates. Taken together, k(red)/K(d) values indicate a minimum 20-fold preference for 2DHNAD. We also offer the first structures of a renalase in complex with catalytically relevant ligands β-NAD⁺ and β-NADH (the latter being an analogue of the substrate(s)). These structures show potential electrostatic repulsion interactions with the product and a unique binding orientation for the substrate nicotinamide base that is consistent with the identified activity.

Renalase does not catalyze the oxidation of catecholamines

It is widely accepted that the function of human renalase is to oxidize catecholamines in blood. However, this belief is based on experiments that did not account for slow, facile catecholamine autoxidation reactions. Recent evidence has shown that renalase has substrates with which it reacts rapidly. The reaction catalyzed defines renalase as an oxidase, one that harvests two electrons from either 2-dihydroNAD(P) or 6-dihydroNAD(P) to form β-NAD(P)(+) and hydrogen peroxide. The apparent metabolic purpose of such a reaction is to avoid inhibition of primary dehydrogenase enzymes by these β-NAD(P)H isomers. This article demonstrates that renalase does not catalyze the oxidation of neurotransmitter catecholamines. Using high-performance liquid chromatography we show that there is no evidence of consumption of epinephrine by renalase. Using time-dependent spectrophotometry we show that the renalase FAD cofactor spectrum is unresponsive to added catecholamines, that adrenochromes are not observed to accumulate in the presence of renalase and that the kinetics of single turnover reactions with 6-dihydroNAD are unaltered by the addition of catecholamines. Lastly we show using an oxygen electrode assay that plasma renalase activity is below the level of detection and only when exogenous renalase and 6-dihydroNAD are added can dioxygen be observed to be consumed.

Renal dopaminergic system: Pathophysiological implications and clinical perspectives

Fluid homeostasis, blood pressure and redox balance in the kidney are regulated by an intricate interaction between local and systemic anti-natriuretic and natriuretic systems. Intrarenal dopamine plays a central role on this interactive network. By activating specific receptors, dopamine promotes sodium excretion and stimulates anti-oxidant and anti-inflammatory pathways. Different pathological scenarios where renal sodium excretion is dysregulated, as in nephrotic syndrome, hypertension and renal inflammation, can be associated with impaired action of renal dopamine including alteration in biosynthesis, dopamine receptor expression and signal transduction. Given its properties on the regulation of renal blood flow and sodium excretion, exogenous dopamine has been postulated as a potential therapeutic strategy to prevent renal failure in critically ill patients. The aim of this review is to update and discuss on the most recent findings about renal dopaminergic system and its role in several diseases involving the kidneys and the potential use of dopamine as a nephroprotective agent.

The catalytic function of renalase: A decade of phantoms

Ten years after the initial identification of human renalase the first genuinely catalytic substrates have been identified. Throughout the prior decade a consensus belief that renalase is produced predominantly by the kidney and catalytically oxidizes catecholamines in order to lower blood pressure and slow the heart has prevailed. This belief was, however, based on fundamentally flawed scientific observations that did not include control reactions to account for the well-known autoxidation of catecholamines in oxygenated solutions. Nonetheless, the initial claims have served as the kernel for a rapidly expanding body of research largely predicated on the belief that catecholamines are substrates for this enzyme. The proliferation of scientific studies pertaining to renalase as a hormone has proceeded unabated despite well-reasoned expressions of dissent that have indicated the deficiencies of the initial observations and other inconsistencies. Our group has very recently identified isomeric forms of β-NAD(P)H as substrates for renalase. These substrates arise from non-specific reduction of β-NAD(P)(+) that forms β-4-dihydroNAD(P) (β-NAD(P)H), β-2-dihydroNAD(P) and β-6-dihydroNAD(P); the latter two being substrates for renalase. Renalase oxidizes these substrates with rate constants that are up to 10(4)-fold faster than any claimed for catecholamines. The electrons harvested are delivered to dioxygen via the enzyme's FAD cofactor forming both H2O2 and β-NAD(P)(+) as products. It would appear that the metabolic purpose of this chemistry is to alleviate the inhibitory effect of β-2-dihydroNAD(P) and β-6-dihydroNAD(P) on primary metabolism dehydrogenase enzymes. The identification of this genuinely catalytic activity for renalase calls for re-evaluation of much of the research of this enzyme, in which definitive links between renalase catecholamine consumption and physiological responses were reported. This article is part of a Special Issue entitled: Physiological enzymology and protein functions.

Effect of Salt Intake and Potassium Supplementation on Urinary Renalase and Serum Dopamine Levels in Chinese Adults

Objective: The aim of our study was to assess the effects of altered salt and potassium intake on urinary renalase and serum dopamine levels in humans. Methods: Forty-two subjects (28-65 years of age) were selected from a rural community of northern China. All subjects were sequentially maintained on a low-salt diet for 7 days (3.0 g/day of NaCl), a high-salt diet for an additional 7 days (18.0 g/day of NaCl), and a high-salt diet with potassium supplementation for a final 7 days (18.0 g/day of NaCl + 4.5 g/day of KCl). Results: Urinary renalase excretions were significantly higher during the high-salt diet intervention than during the low-salt diet. During high-potassium intake, urinary renalase excretions were not significantly different from the high-salt diet, whereas they were significantly higher than the low-salt levels. Serum dopamine levels exhibited similar trends across the interventions. Additionally, a significant positive relationship was observed between the urine renalase and serum dopamine among the different dietary interventions. Also, 24-hour urinary sodium excretion positively correlated with urine renalase and serum dopamine in the whole population. Conclusions: The present study indicates that dietary salt intake and potassium supplementation increase urinary renalase and serum dopamine levels in Chinese subjects.

Renalase contributes to the renal protection of delayed ischaemic preconditioning via the regulation of hypoxia-inducible factor-1α

Ischaemic preconditioning (IPC) attenuates acute kidney injury (AKI) from renal ischaemia reperfusion. Renalase, an amine oxidase secreted by the proximal tubule, not only degrades circulating catecholamines but also protects against renal ischaemia reperfusion injury. Here, it has been suggested that the renoprotective effect of renal IPC is partly mediated by renalase. In a model of brief intermittent renal IPC, the increased cortex renalase expression was found to last for 48 hrs. IPC significantly reduced renal tubular inflammation, necrosis and oxidative stress following renal ischaemia reperfusion injury. Such effects were attenuated by blocking renalase with an anti-renalase monoclonal antibody. We further demonstrated that renalase expression was up-regulated by hypoxia in vitro via an hypoxia-inducible factor (HIF)-1α mechanism. The IPC-induced up-regulation of renalase in vivo was also reduced by pre-treatment with an HIF-1α inhibitor, 3-(5′-Hydroxymethyl-2′-furyl)-1-benzyl indazole. In summary, the renoprotective effect of IPC is partly dependent on the renalase expression, which may be triggered by hypoxia via an HIF-1α mechanism. Endogenous renalase shows potential as a therapeutic agent for the prevention and treatment of AKI.

Renalase, kidney and cardiovascular disease: are they related or just coincidentally associated?

Cardiovascular diseases, including hypertension are the leading cause of death in the developed countries. Diabetes and chronic kidney disease became also more prevalent reaching almost the level of epidemy. Researchers are looking eagerly for the new risk and/or pathogenetic factors, as well as therapeutic option in these disease. It has been suggested that human kidney releases a protein named renalase into the bloodstream. It is supposed to be an enzyme which breaks down catecholamines in the blood circulation and regulate blood pressure. However, there were several doubts whether renalase exerts monoaminooxidase activity, or if it is monoaminooxidase at all. Recently, a hypothesis that it is also a cytokine was postulated. Studies on renalase polymorphisms in hypertension, cardiovascular disease or diabetes are inconsistent. Similarly, there are several discrepancies in the animal on the possible role of renalase in hypertension and cardiovascular diseases. Some studies report a protective role of renalase in acute kidney injury, whereas others showed that renalase levels were mainly dependent on kidney function, indicating rather a role of kidney in excretion of this substance. Moreover, validated assays are needed to evaluate renalase levels and activity. On one hand a deeper and more accurate link between renalase and cardiovascular diseases require further profound research, on the other hand whether or not renalase protein could be a new therapeutic target in these pathologies should also be considered. Whether renalase, discovered in 2005, might be a Holy Grail of hypertension, linking kidney and cardiovascular diseases, remains to be proven.

Proteomic basis of stress responses in the gills of the pacific oyster Crassostrea gigas

The Pacific oyster Crassostrea gigas is one of the dominant sessile inhabitants of the estuarine intertidal zone, which is a physically harsh environment due to the presence of a number of stressors. Oysters have adapted to highly dynamic and stressful environments, but the molecular mechanisms underlying such stress adaptation are largely unknown. In the present study, we examined the proteomic responses in the gills of C. gigas exposed to three stressors (high temperature, low salinity, and aerial exposure) they often encounter in the field. We quantitatively compared the gill proteome profiles using iTRAQ-coupled 2-D LC-MS/MS. There were 3165 identified proteins among which 2379 proteins could be quantified. Heat shock, hyposalinity, and aerial exposure resulted in 50, 15, and 33 differentially expressed gill proteins, respectively. Venn diagram analysis revealed substantial different responses to the three stressors. Only xanthine dehydrogenase/oxidase showed a similar expression pattern across the three stress treatments, suggesting that reduction of ROS accumulation may be a conserved response to these stressors. Heat shock caused significant overexpression of molecular chaperones and production of S-adenosyl-l-methionine, indicating their crucial protective roles against protein denature. In addition, heat shock also activated immune responses, Ca(2+) binding protein expression. By contrast, hyposalinity and aerial exposure resulted in the up-regulation of 3-demethylubiquinone-9 3-methyltransferase, indicating that increase in ubiquinone synthesis may contribute to withstanding both the osmotic and desiccation stress. Strikingly, the majority of desiccation-responsive proteins, including those involved in metabolism, ion transportation, immune responses, DNA duplication, and protein synthesis, were down-regulated, indicating conservation of energy as an important strategy to cope with desiccation stress. There was a high consistency between the expression levels determined by iTRAQ and Western blotting, highlighting the high reproducibility of our proteomic approach and its great value in revealing molecular mechanisms of stress responses.

Renalase regulates peripheral and central dopaminergic activities

Renalase is a recently identified FAD/NADH-dependent amine oxidase mainly expressed in kidney that is secreted into blood and urine where it was suggested to metabolize catecholamines. The present study evaluated central and peripheral dopaminergic activities in the renalase knockout (KO) mouse model and examined the changes induced by recombinant renalase (RR) administration on plasma and urine catecholamine levels. Compared with wild-type (WT) mice, KO mice presented increased plasma levels of epinephrine (Epi), norepinephrine (NE), and dopamine (DA) that were accompanied by increases in the urinary excretion of Epi, NE, DA. In addition, the KO mice presented an increase in urinary DA-to-l-3,4-dihydroxyphenylalanine (l-DOPA) ratios without changes in renal tubular aromatic-l-amino acid decarboxylase (AADC) activity. By contrast, the in vivo administration of RR (1.5 mg/kg sc) to KO mice was accompanied by significant decreases in plasma levels of Epi, DA, and l-DOPA as well as in urinary excretion of Epi, DA, and DA-to-l-DOPA ratios notwithstanding the accompanied increase in renal AADC activity. In addition, the increase in renal DA output observed in renalase KO mice was accompanied by an increase in the expression of the L-type amino acid transporter like (LAT) 1 that is reversed by the administration of RR in these animals. These results suggest that the overexpression of LAT1 in the renal cortex of the renalase KO mice might contribute to the enhanced l-DOPA availability/uptake and consequently to the activation of the renal dopaminergic system in the presence of renalase deficiency.

Signaling pathways involved in renal oxidative injury: role of the vasoactive peptides and the renal dopaminergic system

The physiological hydroelectrolytic balance and the redox steady state in the kidney are accomplished by an intricate interaction between signals from extrarenal and intrarenal sources and between antinatriuretic and natriuretic factors. Angiotensin II, atrial natriuretic peptide and intrarenal dopamine play a pivotal role in this interactive network. The balance between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide, by one side, and the prooxidant effect of the renin angiotensin system, by the other side, contributes to ensuring the normal function of the kidney. Different pathological scenarios, as nephrotic syndrome and hypertension, where renal sodium excretion is altered, are associated with an impaired interaction between two natriuretic systems as the renal dopaminergic system and atrial natriuretic peptide that may be involved in the pathogenesis of renal diseases. The aim of this review is to update and comment the most recent evidences about the intracellular pathways involved in the relationship between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide and the prooxidant effect of the renin angiotensin system in the pathogenesis of renal inflammation.

Concepts of scientific integrative medicine applied to the physiology and pathophysiology of catecholamine systems

This review presents concepts of scientific integrative medicine and relates them to the physiology of catecholamine systems and to the pathophysiology of catecholamine-related disorders. The applications to catecholamine systems exemplify how scientific integrative medicine links systems biology with integrative physiology. Concepts of scientific integrative medicine include (i) negative feedback regulation, maintaining stability of the body's monitored variables; (ii) homeostats, which compare information about monitored variables with algorithms for responding; (iii) multiple effectors, enabling compensatory activation of alternative effectors and primitive specificity of stress response patterns; (iv) effector sharing, accounting for interactions among homeostats and phenomena such as hyperglycemia attending gastrointestinal bleeding and hyponatremia attending congestive heart failure; (v) stress, applying a definition as a state rather than as an environmental stimulus or stereotyped response; (vi) distress, using a noncircular definition that does not presume pathology; (vii) allostasis, corresponding to adaptive plasticity of feedback-regulated systems; and (viii) allostatic load, explaining chronic degenerative diseases in terms of effects of cumulative wear and tear. From computer models one can predict mathematically the effects of stress and allostatic load on the transition from wellness to symptomatic disease. The review describes acute and chronic clinical disorders involving catecholamine systems-especially Parkinson disease-and how these concepts relate to pathophysiology, early detection, and treatment and prevention strategies in the post-genome era.

Renalase, a new secretory enzyme: Its role in hypertensive-ischemic cardiovascular diseases

Abstract Renalase, a novel amine oxidase, is mainly expressed in the kidney, heart, and skeletal muscle. It has been known to degrade circulating catecholamines and plays a crucial role in human diseases. Recent studies have demonstrated its structure, unique bioactivities, function, and the gene polymorphisms in human diseases. In this review, we summarize the effects of renalase on hypertension, myocardial ischemia, acute kidney injury (AKI), ischemic stroke, cardiac dysfunction, organ transplantation, and diabetes mellitus reported in numerous studies.

Plasma and urine renalase levels and activity during the recovery of renal function in kidney transplant recipients

Renalase is a recently described enzyme secreted by the kidney into both plasma and urine, where it was suggested to degrade catecholamines contributing to blood pressure control. While there is a controversy regarding the relationship between renal function and plasma renalase levels, there is virtually no data in humans on plasma renalase activity as well as on both urine renalase levels and activity. We prospectively examined the time course of plasma and urine renalase levels and activity in 26 end-stage renal disease (ESRD) patients receiving a cadaver kidney transplant (cadaver kidney recipients [CKR]) before surgery and during the recovery of renal function up to day 90 post transplant. The relationship with sympathetic and renal dopaminergic activities was also evaluated. The recovery of renal function in CKR closely predicted decreases in plasma renalase levels ( r = 0.88; P < 0.0001), urine renalase levels ( r = 0.75; P < 0.0001) and urine renalase activity ( r = 0.56; P < 0.03), but did not predict changes in plasma renalase activity ( r = −0.02; NS). Plasma norepinephrine levels positively correlated with plasma renalase levels ( r = 0.64, P < 0.002) as well as with urine renalase levels and activity ( r = 0.47 P < 0.02; r = 0.71, P < 0.0005, respectively) and negatively correlated with plasma renalase activity ( r = −0.57, P < 0.002). By contrast, plasma epinephrine levels positively correlated with plasma renalase activity ( r = 0.67, P < 0.0001) and negatively correlated with plasma renalase levels ( r = −0.62, P < 0.003). A significant negative relationship was observed between urine dopamine output and urine renalase levels ( r = −0.48; P < 0.03) but not with urine renalase activity ( r = −0.33, NS). We conclude that plasma and urine renalase levels closely depend on renal function and sympathetic nervous system activity. It is suggested that epinephrine-mediated activation of circulating renalase may occur in renal transplant recipients with good recovery of renal function. The increase in plasma renalase activity observed in ESRD patients and renal transplant recipients can be explained on the basis of reduced inhibition of the circulating enzyme.

Regulation of renalase expression by D5 dopamine receptors in rat renal proximal tubule cells

The dopaminergic and sympathetic systems interact to regulate blood pressure. Our previous studies showed regulation of α1-adrenergic receptor function by D1-like dopamine receptors in vascular smooth muscle cells. Because renalase could regulate circulating epinephrine levels and dopamine production in renal proximal tubules (RPTs), we tested the hypothesis that D1-like receptors regulate renalase expression in kidney. The effect of D1-like receptor stimulation on renalase expression and function was measured in immortalized RPT cells from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). We found that the D1-like receptor agonist fenoldopam (10(-7)-10(-5) mol/l) increased renalase protein expression and function in WKY RPT cells but decreased them in SHR cells. Fenoldopam also increased renalase mRNA levels in WKY but not in SHR cells. In contrast, fenoldopam increased the degradation of renalase protein in SHR cells but not in WKY cells. The regulation of renalase by the D1-like receptor was mainly via the D5 receptor because silencing of the D5 but not D1 receptor by antisense oligonucleotides blocked the stimulatory effect of the D1-like receptor on renalase expression in WKY cells. Moreover, inhibition of PKC, by the PKC inhibitor 19-31, blocked the stimulatory effect of fenoldopam on renalase expression while stimulation of PKC, by a PKC agonist (PMA), increased renalase expression, indicating that PKC is involved in the process. Our studies suggest that the D5 receptor positively regulates renalase expression in WKY but not SHR RPT cells; aberrant regulation of renalase by the D5 receptor may be involved in the pathogenesis of hypertension.

Renalase in hypertension and kidney disease

Renalase, a recently discovered flavoprotein, which is strongly expressed in the kidney and heart, effectively metabolizes catecholamines. It was discovered during the search to identify proteins secreted by the kidney that could help explain the high incidence of cardiovascular disease in patients with chronic kidney disease. Recent advances have led to more detailed knowledge of its biology, structure, enzymatic activity, mechanisms of action, associations with human disease states and potential therapeutic value. In this study, we review these advances with a focus on hypertension and kidney disease.

Sodium-dependent modulation of systemic and urinary renalase expression and activity in the rat remnant kidney

OBJECTIVE

The present study examined the influence of high-sodium intake on systemic and urinary renalase levels and activity in 3/4 nephrectomized (3/4nx) and Sham rats.

RESULTS

The reduced circulating renalase levels in 3/4nx rats during normal-sodium intake were accompanied by increased plasma renalase activity. The sodium-induced increase of blood pressure in 3/4nx rats was accompanied by significant decreases in circulating renalase levels and activity as well as by a significant decrease in cardiac renalase levels in 3/4nx rats but not in Sham rats. During normal-sodium intake, no significant differences were observed in either urine renalase levels or activity between 3/4nx and Sham rats, not withstanding the ∼75% decrease in daily urine dopamine output observed in the rat remnant kidney. During high-sodium intake, urinary renalase levels increased in both 3/4nx and Sham groups by three-fold whereas urinary renalase activity increased in 3/4nx and Sham rats by greater than twelve-fold and greater than four-fold, respectively. This was accompanied by sodium-induced increases in daily urinary dopamine output in both 3/4nx and Sham rats by ∼2.3-fold and ∼1.6-fold, respectively.

CONCLUSION

The reduced circulating renalase levels in 3/4nx rats are accompanied by increased plasma renalase activity, which appears to be related with decreased inhibition of the circulating enzyme. Differences in systemic and urinary renalase levels and activity between 3/4nx and Sham rats during high-sodium intake may contribute to activation of the sympathetic nervous system, hypertension and enhanced cardiovascular risk in CKD but do not appear to account for the decrease in renal dopaminergic activity in the rat remnant kidney.

Renalase is an α-NAD(P)H oxidase/anomerase

Renalase is a protein hormone secreted into the blood by the kidney that is reported to lower blood pressure and slow heart rate. Since its discovery in 2005, renalase has been the subject of conjecture pertaining to its catalytic function. While it has been widely reported that renalase is the third monoamine oxidase (monoamine oxidase C) that oxidizes circulating catecholamines such as epinephrine, there has been no convincing demonstration of this catalysis in vitro. Renalase is a flavoprotein whose structural topology is similar to known oxidases, lysine demethylases, and monooxygenases, but its active site bears no resemblance to that of any known flavoprotein. We have identified the catalytic activity of renalase as an α-NAD(P)H oxidase/anomerase, whereby low equilibrium concentrations of the α-anomer of NADPH and NADH initiate rapid reduction of the renalase flavin cofactor. The reduced cofactor then reacts with dioxygen to form hydrogen peroxide and releases nicotinamide dinucleotide product in the β-form. These processes yield an apparent turnover number (0.5 s(-1) in atmospheric dioxygen) that is at least 2 orders of magnitude more rapid than any reported activity with catechol neurotransmitters. This highly novel activity is the first demonstration of a role for naturally occurring α-NAD(P)H anomers in mammalian physiology and the first report of a flavoprotein catalyzing an epimerization reaction.

Renalase regulates renal dopamine and phosphate metabolism

Renalase is a kidney-secreted catecholamines-degrading enzyme whose expression and activity are downregulated by increased dietary phosphate. A renalase knockout (KO) mouse model was used to explore the mechanisms mediating renalase's effect on phosphate excretion. Compared with wild-type (WT) mice maintained on a regular diet, KO mice show decreased serum PO4(-) (KO = 5.3 ± 0.2 vs. WT = 6.0 ± 0.1, n = 6; P < 0.04) and increased urinary PO4(-) excretion (urine PO4(-)/creatinine: KO = 7.7 ± 0.3 vs. WT = 6.1 ± 0.3, n = 6; P < 0.02). However, both WT and KO mice respond similarly to PO4(-) restriction by increasing renal COMT-1 activity and markedly decreasing PO4(-) excretion, which excludes an intrinsic renal defect in the KO. Renal sodium-phosphate cotransporter Npt2a, sodium proton exchanger NHE3 expression, and MAO-A and B activity did not differ between WT and KO. Only catechol-O-methyl transferase (COMT) expression and activity were significantly increased in KO mice. Despite that, urinary dopamine increased by twofold, whereas urinary l-DOPA excretion decreased by twofold in the KO mouse, indicating an upregulation of renal dopamine (DA) synthesis. These data indicate that renalase deficiency is associated with increased renal DA synthesis, stimulated PO4(-) excretion, and moderately severe hypophosphatemia. The signal to increase renal DA synthesis is strong since it overcomes a compensatory increase in COMT activity.

Proximal nephron

The kidney plays a fundamental role in maintaining body salt and fluid balance and blood pressure homeostasis through the actions of its proximal and distal tubular segments of nephrons. However, proximal tubules are well recognized to exert a more prominent role than distal counterparts. Proximal tubules are responsible for reabsorbing approximately 65% of filtered load and most, if not all, of filtered amino acids, glucose, solutes, and low molecular weight proteins. Proximal tubules also play a key role in regulating acid-base balance by reabsorbing approximately 80% of filtered bicarbonate. The purpose of this review article is to provide a comprehensive overview of new insights and perspectives into current understanding of proximal tubules of nephrons, with an emphasis on the ultrastructure, molecular biology, cellular and integrative physiology, and the underlying signaling transduction mechanisms. The review is divided into three closely related sections. The first section focuses on the classification of nephrons and recent perspectives on the potential role of nephron numbers in human health and diseases. The second section reviews recent research on the structural and biochemical basis of proximal tubular function. The final section provides a comprehensive overview of new insights and perspectives in the physiological regulation of proximal tubular transport by vasoactive hormones. In the latter section, attention is particularly paid to new insights and perspectives learnt from recent cloning of transporters, development of transgenic animals with knockout or knockin of a particular gene of interest, and mapping of signaling pathways using microarrays and/or physiological proteomic approaches.

Renalase protects against ischemic AKI

Elevated levels of plasma catecholamines accompany ischemic AKI, possibly contributing the inflammatory response. Renalase, an amine oxidase secreted by the proximal tubule, degrades circulating catecholamines and reduces myocardial necrosis, suggesting that it may protect against renal ischemia reperfusion injury. Here, mice subjected to renal ischemia reperfusion injury had significantly lower levels of renalase in the plasma and kidney compared with sham-operated mice. Consistent with this, plasma NE levels increased significantly after renal ischemia reperfusion injury. Furthermore, renal tubular inflammation, necrosis, and apoptosis were more severe and plasma catecholamine levels were higher in renalase-deficient mice subjected to renal ischemia reperfusion compared with wild-type mice. Administration of recombinant human renalase reduced plasma catecholamine levels and ameliorated ischemic AKI in wild-type mice. Taken together, these data suggest that renalase protects against ischemic AKI by reducing renal tubular necrosis, apoptosis, and inflammation, and that plasma renalase might be a biomarker for AKI. Recombinant renalase therapy may have potential for the prevention and treatment of AKI.

Renal dopamine and angiotensin II receptor signaling in age-related hypertension

Kidneys play a vital role in long-term regulation of blood pressure. This is achieved by actions of many renal and nonrenal factors acting on the kidney that help maintain the body's water and electrolyte balance and thus control blood pressure. Several endogenously formed or circulating hormones/peptides, by acting within the kidney, regulate fluid and water homeostasis and blood pressure. Dopamine and angiotensin II are the two key renal factors that, via acting on their receptors and counterregulating each other's function, maintain water and sodium balance. In this review, we provide recent advances in the signaling cascades of these renal receptors, especially at the level of their cross talk, and discuss their roles in blood pressure regulation in the aging process.

Renalase's expression and distribution in renal tissue and cells

To study renalase's expression and distribution in renal tissues and cells, renalase coded DNA vaccine was constructed, and anti-renalase monoclonal antibodies were produced using DNA immunization and hybridoma technique, followed by further investigation with immunological testing and western blotting to detect the expression and distribution of renalase among the renal tissue and cells. Anti-renalase monoclonal antibodies were successfully prepared by using DNA immunization technique. Further studies with anti-renalase monoclonal antibody showed that renalase expressed in glomeruli, tubule, mesangial cells, podocytes, renal tubule epithelial cells and its cells supernatant. Renalase is wildly expressed in kidney, including glomeruli, tubule, mesangial cells, podocytes and tubule epithelial cells, and may be secreted by tubule epithelial cells primarily.